In the emissive portion of the spectrum, it is necessary to create an approximation of the ultimate reference, the classical Planck “blackbody.” The blackbody is an ideal (not perfectly attainable) device that can remain at constant temperature in thermal isolation while absorbing radiative power at visible to SWIR wavelengths. It does this by emitting the same power at longer wavelengths, because otherwise its temperature would rise. The Kirchoff expression “power emitted = power incident” defines a blackbody. A greybody, on the other hand, reflects some incident light, and the Kirchoff expression includes the reflectance and a multiplicative factor in front of the emission term called the “emissivity,” which is less than unity, indicating that the device is not emitting the same power incident on the device. Were it possible to create a perfect blackbody, then a superb emissive spectral band calibration reference could be built, because the emission from a blackbody at any temperature is perfectly defined by the Planck radiation law. The approach would be to measure the emission of the blackbody at a series of temperatures covering the range of anticipated Earth scene temperatures. The known blackbody emission provides a “universal” reference frame, and the only problem left is to ensure that the temperature is well known.

Obtaining Inter-Comparable Data Sets

Polar and geostationary satellite data already constitute the vast majority of the data ingested in NWP models. As these systems are improved, the ability to extend severe storm forecasts for the United States depends on consistent radiometry between current and future systems, and between the next-generation POES (NPOESS) and GOES (GOES-R) systems. Further success in extending severe storm warnings across the globe to benefit all nations will depend on extending the benefits of U.S. environmental satellite calibration consistency to other international satellite systems.



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